(a) Field of the Invention
The present invention relates to a transflective liquid crystal display or a reflective liquid crystal display.
(b) Description of the Related Art
Generally, a liquid crystal display (LCD) includes a pair of panels individually having electrodes on their inner surfaces, and a dielectric anisotropy liquid crystal (LC) layer interposed between the panels. In an LCD, a variation of a voltage difference between the field generating electrodes, i.e., a variation in the strength of an electric field generated by the electrodes, changes the transmittance of light passing through the LCD, and thus desired images are obtained by controlling the voltage difference between the electrodes.
Depending on the kinds of light source used for image display, LCDs are divided into three types: transmissive, reflective, and transflective. In transmissive LCDs, pixels are illuminated from behind using a backlight. In reflective LCDs, the pixels are illuminated from the front using incident light originating from the ambient environment. The transflective LCDs combine transmissive and reflective characteristics. Under medium light conditions such as in an indoor environment, or under complete darkness conditions, these LCDs are operated in a transmissive mode, while under very bright conditions such as in an outdoor environment, they are operated in a reflective mode.
In the reflective LCDs and the transflective LCDs, two absorbing polarizers, which are films produced by adding iodine molecules or bichromatic dyes to stretched PVA, are individually attached to the outer surfaces of the panels. In general, the absorbing polarizers have unique optical characteristics. That is, they allow only P-waves of incident light to pass and absorb S-waves. Theoretically, an absorbing polarizer transmits 50% of incident light and absorbs the remaining 50%. However, the absorbing polarizer actually transmits only 43% to 45% due to a light loss at its surface. In the case when the light passing through the absorbing polarizer is returned to the same polarizer again by reflection at a reflective electrode, the transmittance of the light passing through the polarizer again is only 39% to 41%, even if the reflectance at the reflective electrode is 100% and the color filters cause no light loss. Accordingly, the actual transmittance is less than 39% to 41% because the color filters used for the color display cause a light loss and also because the actual reflectance at the reflective electrode is not 100%.